An aircraft landing gear assembly is generally movable between a deployed condition, for take-off and landing, and a stowed condition for flight.
An actuator is provided for moving the landing gear between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator, and more than one can be provided. A retraction actuator may have one end coupled to the airframe and another end coupled to the main strut such that extension and retraction of the actuator results in movement of the main strut between deployed and stowed conditions.
A brace or stay is generally provided to support the orientation of the main fitting when the landing gear is in the deployed condition. A stay generally includes a two bar linkage that can be unfolded to assume a generally aligned, over centre condition in which the stay is locked to inhibit movement of the main fitting. When the stay is broken, it no longer reacts movement of the main fitting and the main fitting can be moved by the retraction actuator to the stowed condition. Some main landing gear assemblies include a pair of stays coupled to a common main fitting.
A lock link is generally provided in conjunction with each stay to maintain the stay in the locked condition. A lock link generally includes a two bar linkage that can be unfolded to assume a locked over centre condition to inhibit movement of the stay. The lock link must be broken to enable the stay to be folded, thereby permitting the main fitting to be moved by the retraction actuator towards the stowed condition.
It is common for a landing gear assembly to be arranged to move towards the deployed condition in the event of a failure of the retraction actuator. Initially, the landing gear assembly will move by way of gravity, and in doing so the stay is forced to move towards the locked condition. One or more down lock springs can be provided, which are arranged to assist in moving the landing gear assembly to the deployed condition and locking it in that state by making the lock link. Down lock springs also inhibit the lock link accidentally being unlocked and consequently it takes a large force to overcome the down lock springs when breaking the alignment of the lock link.
It is therefore known to provide a hydraulic actuator to move the lock link between the locked over centre condition and the unlocked broken condition.
In order to simplify the management and power sources for the various actuators found on an aircraft, the present inventors have sought to replace hydraulic actuators with electric or electromechanical actuators.
However, a problem exists in that failure of an electromechanical actuator generally results in the actuator locking, which could inhibit the landing gear assembly assuming the deployed condition in the event of failure of the electromechanical actuator.